This invention relates to a method of rolling rails, and more particularly to a method of rolling rails using continuous rolling mills, including a universal mill, for H-sections.
Generally, universal rolling is divided into two steps; one is a process in which bloom is processed through pass grooves in two horizontal rolls and the other is a process in which the thus processed bloom, or breakdown, is further processed into the desired product through universal stands. The former is known as the roughing process and the latter as the universal process. Application of universal rolling to rails has brought about a considerable cutback in production cost and a remarkable improvement in quality and dimensional accuracy, compared with the conventional passgroove rolling method. However, the roughing process needs special operating techniques such as reduction, upsetting, twisting and turning. Besides, as many as 12 to 14 passes must be made through the pass grooves in the rolls on the two roughing stands, the time for this roughing operation accounting for approximately 70 percent of the total pass time for each rail.
FIG. 1a shows a rail-rolling mill train of the conventional type and the arrangement of the roll passes thereof. This rail mill consists of two breakdown stands BD.sub.1 and BD.sub.2, a four-roll universal stand U.sub.1, an edger stand E, a four-roll universal stand U.sub.2, a head-wheel stand H, and a base-wheel stand B. Thus, universal rolling consists of four steps; four-roll universal stand rolling aimed principally at elongation, edger rolling, head-wheel rolling and base-wheel rolling aimed principally at reforming. With a greater portion of reduction of the head and base carried out by the four-roll universal stand in the direction of thickness, the breakdown obtained in this method has a larger section that is substantially similar to the desired rail in shape, as shown in FIG. 2a. In order to obtain the breakdown shaped like this, the difference in width between the head and base must be accomplished in the roughing operation, as indicated by the pass grooves on the roughing stands BD.sub.1 and BD.sub.2. This calls for providing many roll passes and installing two roughing stands BD.sub.1 and BD.sub.2 one after the other. As a consequence, the amount which can be produced in the roughing operation governs the productivity of the universal rail rolling operation as a whole.
Meanwhile, it is well-known that H-sections can be continuously manufactured by making only a single pass through such universal stands as stands B.sub.1 ', U.sub.1, U.sub.2, B.sub.2 ', U.sub.3, B.sub.3 ', edger stands E, H.sub.1 ', H.sub.2 ', and so on after a breakdown stand BD. It is preferable to roll rails using such a continuous H-section mill since it provides various advantages including the integration of mills.